Recently, a GUI becomes enhanced, and a technique of outputting an execution result of a computer program by an image is also known. Further, in developing a system for a computer or the like, a test for checking whether or not the system normally operates is conventionally performed. Execution of the test has a problem of a burden put on a test manager such as preparation for the test, execution of the test, checking of results and so on. Hence, recently, a simple test by image comparison is increasingly performed. Patent Literature 1 discloses a technique of verifying an execution result of a computer program by image comparison. The technique in Patent Literature 1 performs image comparison after removing designated mask regions from two images created by the execution of the computer program respectively, and displays a comparison result.